Snap-action switch



NOV. 5, 1940- c. G. KRONMILLER 2,220,802

SNAP-ACTION SWITCH Filed Jan. 13, 1958 '74 37 r 'r1 3 g 232,32 o 392o 77 5'( INVENTOR Curl Kronmiller Ei .3 BY/fpm, Amm@ ATTORNEY Patented Nov. 5, 1940 UNITED STATE PATENT OFFICE SNAP-CTIN SWITCH Application January iii, i938, Serial No. lillil Claims.

'I'his invention relates broadly to a switching mechanism and more particularly to a snapacting switch which is operated in response to some condition such as temperature or'pressure to open a set of contacts. For purposes of illustration only the device will be described as being responsive to pressure, but it is to be distinctly understood that it may be just as easily made to respond to temperature.

An object of this invention is to provide a switch which will open its contacts when the pressure to which it responds reaches a predetermined point.

A further object is to provide a pressure responsive switch which vmay be adapted to break the circuit to an operating device upon the occurrence of a high pressure which indicates a dangerous condition in saidl device.

A further object of the invention is to provide a high pressure cut-out switch which will automatically return to closed-circuit position upon a drop in pressure to a value which is below that which caused switch opening.

Another object is to provide a snap-action mechanism operated by a condition responsive device for opening a switch, with additional means also operated by said condition responsive mechanism for positively opening said switch in case said snap acting mechanism should iail for some reason.

A still further object is to provide a high pressure switch which will cut out at a high pressure and cut in again when the pressure drops to a predetermined lower value and which has a means for adjusting this differential.

Another object of this invention is to provide a switchl which will cut out at a high pressure and which will attempt to close at a predetermined lower pressure but which has a stop for preventing such closure, and a manual means for resetting the switch to closed position after it has once cut out.

Still another object is to provide a high pressure cut-out switch which has a main adjustment'spring for adjusting the cut-in pressure and also a compression pick-up spring for adjusting the difference between the cut-in and cutout pressures of the switch.

Other objects will become apparent upon a study of the following specification in connection with the drawing, in which Figure `1 is a rear view in elevation with parts broken away showing the main adjusting spring and compression pick-up spring;

Mgure 2 is a sectional view taken substantially along the lines 2--2 of Figure 1;

Figure 3 is a detail view taken substantially along the lines 3 3 o Figure l showing the manual reset mechanism and the positive switch opener; and

Figures l and 5 are more or less diagrammatic views showing two operating positions of the device.

Referring to Figures l and 2 of the drawing,

itwill be noted that the present device is supported on a base plate ii from which depends a casing i2 which houses a bellows or some similar pressure responsive device (not shown). Attached to the bottom of casing i2 is a nipple iii which may be connected to the source of pressure tc which the device is intended to respond, or in the case of a temperature responsive device it will be connected to a thermal bulb by means of a capillary tube. On top of the base plate i i are two upstanding brackets M and i5 which are mounted on the base by means of anges i6 and il. It will be noted that casing i2 is provided with a circular flange i8 and that screws i9 extend through this ange, through the base plate, and through the flanges I6 and il to hold the casing, base plate and brackets in assembled relation. At their top the two brackets i4 and i5 are joined together by a connecting member 2li, which member has a portion 2i (Figure 2) which extends downwardly at the rear of the device and which has an inwardly extending portion 92 at the bottom thereof for a purpose' to be described later. Extending upwardly through a hole in the base plate il is a pin 23 which is adapted to be connected to the pressure responsive device within the casing I2 and operated thereby. Mounted on pin 23 is a cone 24 adapted to seat in a dwell in an operating lever 25. Extending between the two brackets Hi and i5 just above lever 25 is a connecting piece having two depending knife edge portions 2l which seat in dwells in opposite sides of the lever 25 and about which this lever is adapted to pivot.

Lever 25 is provided with a forked arm 128 in 4 when screw 34 is rotated, which will therefore cause a vertical movement of the nut and a cony sequent adjustment of the tension of spring .29.

It will be noted that the effect of this spring 29 is to oppose rotation of lever 25 by the pressure responsive device in a counter-clockwise direction and constitutes the main setting for the device. A second `:rew 36 depends loosely through a hole 31 in the connecting member 20, which screw also has thereon a nut 38 having an extending arm 39 for cooperation with a slot in the depending portion of the connecting member 20. As in the case of screw 32, the rotation of screw 36 will cause a vertical adjustment of nut 38. Loosely abutting the bottom of nut 38 is a spring 40 which loosely surrounds screw 36 and whose lower end rests against the top of the inturned portion 22 of the connecting member 20, which has a hole 4I therein through which stem 42 of screw 36 loosely extends. Mounted on stem 42 just below the inturned portion 22 is a nut 43 which may be adjustably positioned thereon and then rmly held in such position by means of a spring washer 44 and lock nut 45. The purpose of this nut is to limit the upward movement of screw 36 through connecting member 20 due to the force exerted on the nut 38 by spring 40. Lever 25 has a notch 46 cut therein through which the lower end of stem 42 extends. Positioned on the lower end of stem 42 below lever 25 is a second adjustably positioned nut 41 having a spring washer 48 and lock nut 49 for maintaining it in its adjusted position. The purpose of this nut will be described in detail later.

Attached to lever 25 by means of screws 50 is an upstanding arm I having an inwardly extending ear 52. Pivoted to brackets I4 and I5 at 53 is a contact carrying lever 55 having a set of movable contacts 56 mounted thereon by means of a resilient mounting 51 and insulation 58. Cooperating with these movable contacts is aJ set of stationary contacts l59 mounted on an insulating block 60 by means of screws 6| and brackets 62. Rotation of lever 55 about its pivot islimited by means of lower stops 63 and upper` stops 64 integrally connected with brackets I4 and I5. Depending from lever arm 55 are two rearwardly extending arms 65 and 66, each having a bifurcated end, the lower part of which carries a dwell 61. There is provided a U-shaped bail 68, each of whose legs has at the extremity thereof a knife edge 69 which seats in the dwell 61. Each leg is further provided with a latterly extending portion which extends between the bifurcations in the ends of the arms65 and 66. The .upper end of the bail member is provided with a hole 1I in which is hooked one end of a spring member 12, the lower end of which is hooked in a hole 13 which is provided in the end of the ear 52. This bail member 68 is adapted to oscillate back and forth about its knife edge and such oscillation is limited in both directions by means of a stop arm 14 having two depending stop elements and 16.

Mounted underneath the connecting member and at one side thereof is a leaf spring 11 having a cut-away portion 18 forming a shoulder. This spring is secured to the connecting member 20 at the end opposite the cut-away portion by means of a screw 19 and the end having the cutaway portion normally bends downwardly away from the cross piece 28. Lever 55 has an upstanding arm 80 which. when lever 55 is in contact closing position. is adapted to extend to a point beneath spring 11 and flexit upwardly toward connecting member 20. Cooperating with the end 18 of the spring member is a rod 8| which is adapted to be moved vertically by hand. This rod 8| has a pin 82 having an enlarged head which extends through a slot 83 in bracket I4 and is adapted to be guided thereby. At the top of rod 8l is an inturned portion 84 which lies just beneath the spring 11 and upon an upward movement is adapted to raise the normally depressed end of this leaf spring. Rod 8| extends loosely through a hole in the base plate I I and at its lower end has an inturned portion 85 by which the rod is manually moved. The upstanding arm 5I has an outwardly extending portion 86 on the upper end thereof for a purpose which will be described later.

Operation The mechanism described is of the type having a double snap action so that the switch contacts may be open in such a manner that they will not be subject to vanishing contact pressure; that is, the pressure forcing the contacts together will not decrease gradually to zero before the mechanism snaps. This double snap action takes place as follows: Referring to Figure 2, it will be noted that the toggle spring 12 is exerting a force on lever 55 through the bail member 68 to the right of the pivot 53. As can be clearly seen in this figure, this force is tending to rotate the contact lever 55 ina clockwise direction which is holding the contacts 56, 59 closed. Assuming now that the upper end of the bail member will move toward the left, it will be seen that the line of force exerted by this bail member will now be moved to the left of pivot 53, as shown diagrammatically in Figure 4, which due to the, action of spring 12 will cause the contact lever 55 to be rotated in a counter-clockwise direction with a snap action. This snap action would occur regardless of the speed with which the bail member is moved, but as will be seen, the bail member itself is moved with a snap action. Looking again at Figure 2, we see that the spring 12 is tending to rotate the bail member in a clockwise direction, such rotation being limited by the stop 16. Assuming now that the ear 52 will move to the left, it will be noted that the spring will very soon pass between the legs of the bail member 68. Suchan action would produce a snapping of the bail in a counterclockwise direction against stop 15, Thus it is seen that there are two distinct snap actions produced, one by the bail member as it snaps from stop 16 to 15 which will itself snap the lever 55 from engagement with the contacts 59 into engagement with the stop 64. On movement of ear 52 to the right a reverse action will take place snapping contacts 56 and 59 closed.

When the pressure to which this device is intended to respond is at a normal value, the parts will be in the position shown in Figures l and 2. It will be noted that the operating lever is in a substantially horizontal position and the slot 46 is spaced from nut 41 on the bottom of screw 36. Spring 29 is tending to rotate the lever about its knife .edges 21,in a clockwise direction and is holding it against cone 24 which is connected to the pressure responsive device. The switch contacts are in closed position and the device controlled thereby is running normally. As the pressure increases from a normal value. lever will be rotated in a counterclockwise direction by pin 23 and cone 24 which will cause the upstanding arm 5I to rotate the ear 52 to the left, as viewed in Figure 2. However, before the spring 'I2 passes through the legs of the bail 68, the sides of the slot 46 in lever 25 will move into engagement with the nut 4l on the stem of screw 36. Before the lever can move further, it is necessary therefore that it push screw 36 in a downwardly direction against the force of the compression spring 40. It is therefore seen that before the device is capable of opening the switch contacts, it must exert a pressure strong enough to oppose the action of both the main adjusting spring 29 and the differential adjusting spring 40. motion of lever 25 in a counter-clockwise direction, the spring 4l)v4 will be compressed and the spring 12 will pass through the legs of the bail causing the double snap action to function .as set forth above and open the contacts 56 and 59. The parts will now assume the position as shown diagrammatically in Figure 4. Lever 55 in rotating in a counter-clockwise direction to open the contacts has also moved its upstanding arm 80 in a rearwardly direction to such an extent that it has passed from beneath the leaf spring 11 and extends into the cut-away part 18, thus permitting the spring to bend in a downwardly direction.

The contacts now being open, the pressure will begin to drop and the first thing thatwill occur will be the lowering of 'the cone 24 by the pressure responsive device. This` will permit spring 29 and spring 48 to start rotating lever 25 in a clockwise direction and the bar 52 will start moving to the right -to again swing the lower end of the spring 12 between the legs of the bail 68. Before -this takes place, however, the screw 36 will rise under the force of its spring`40 to such an extent that the adjustable nut 43 will strike against the bottom of the inturned portion 22 of the connecting piece 28. This will cause the screw 36 to stop and the sides of slot 46 in the lever 25 will become disengaged therefrom and will be raised further by means of the spring 29 only. Continued rotation of lever 25 in a clockwise direction will eventually cause the ear 52 to pass the lower end of spring 12 between the legs of bail 68 which will cause the bail to snap to the right against stop 16. This action `will now align -the force which is exerted by the bail 68 on the opposite side of the pivot 53 of lever 55 and will therefore tend to rotate this lever in a 'clockwise direc-tion. The upstanding arm 88 on the lever 55 prevents such clockwise rotation due to the fact that it has engaged the shoulder of the cut-away portion 18 of the leaf spring 11, and therefore no matter what the pressure in the device the contacts are incapable of automatically closing. In order to close the contacts atthis time, it is necessary to manually raise the rod 8| causing the inturned portion 84 to engage beneath the end of leaf spring 11 and raise it out of engagement with the arm 80. After this has been done, the force exerted by the spring 12 and bail 68 on the lever 55 will cause the contacts 56, 59 to close with a snap.

In some instances it might occur that this snap-action mechanism would fail, due perhaps to the breakage of spring 12, and in this case it would be dangerous not to open the contacts 56, 59 on a rise in pressure to the control point. To take care of this case, the arm 5I has been provided with an inturned `portion 86 which, on a pressure rise and a subsequent counte'rrclock- Upon continued wise rotation of the lever 25, assuming that the snap-action mechanism has not opened the switch contacts, will strike arm 88 of the lever 55 and swing this lever to open contact position. It will be noted that the manual reset feature will prevent switch closing movement in this case as in the case where the switch was opened by the snap action mechanism.

In some instances it might be desired to eliminate the manual reset feature and provide a device which is completely automatic, that is, one which will open the contacts on the occurrence of a predetermined pressure and will auto- Ymatically close the contacts again upon the occurrence .of a predetermined lower pressure. If a device of this type is desired, it is only necessary to remove screw 'i9 and leaf spring 11. It is now seen that there is nothing to prevent the contact lever 55 from closing the contacts on a subsequent reduction of pressure. In such a device it would be highly desirable to adjust the differential between the contact opening pressure and the contact closing pressure. It will be noted that the spring 29 constantly opposes counter-clockwise rotation of lever 25 by the 'pressure responsive device and adjusting the tension of this spring will adjust the main setting of the device. However, as set forth above, spring 48 must be compressed a certain amount before the snap-action mechanism will cause switch opening. Therefore, the switch opening pressure is determined by the sum of the effects of the spring 29 and the spring 40. Also as set forth above, it was pointed out that before the snap-action mechanism caused closing of the contacts the screw 36 and its spring 48 is released by lever 25 so that the contact closing pressure is determined only by the setting .of the spring 29. Adjustment of the amount of compression of spring 40 will adjust the amount of force which the pressure responsive device must overcome in addition to the force exerted by the spring 29 to cause the contacts to open, and therefore the adjustment of this spring will adjust the difference between the contact opening pressure and the contact closing pressure which is the differential of the device.

It will be noted that where the manual reset feature is used, the pressure must drop to its predetermined lower point before lthe contacts may be manually reset to closed position following a movement of the snap-action mechanism to a switch opening position. This is a desir able feature in that it will prevent any -one from manually holding the contacts closed until after the pressure has dropped to a safe value.

Therefore it will be seen that I have devised a simple device having a minimum number of parts and one which is easy to manufacture. I have also provided a device that may be used to automatically open a switch on a high pressure and which may require that the switch be manually reset following a pressure decrease, or it may be used as a completely automatic device which will return the contacts to closed position automatically upon a decrease in pressure. I have further provided a device having a manual reset which is fool-proof in that the contacts cannot be manually closed until after the pressure has returned-tto a safe value.

Certain changes and modifications of this invention will become apparent to those skilled in the art, and it is therefore to be understood that I am to be limited only by the scope of the appended claims and not by the particular embodiment of this invention described.

The device disclosed in this application is of the same general type as that disclosed in a copending application of AlbertvL. Judson, Serial No. 184,812 and led of even date herewith.

I claim as my invention:

1. In a mechanism of the class described, a snap-action mechanism, a condition responsive device for actuating said mechanism, a control device, a member operated by said snap-action mechanism for operating said control device, a resilient stop comprising a normally bowed leaf spring anchored at one end and free to ex at the other, said spring normally projecting into the path of said member to offer endwise resistance to said member and prevent its operation by said snap-action mechanism in one direction, manual means for exing said spring out 0f the way to permit such operation, and means on said member for flexing said spring out of the way as said member is operated in the oppositedirection by said snap-action mechanism.

2. In a device of the class described comprising a lever pivoted for rotation between fixed stops, a condition responsive device for rotating said lever from one ixed stop to the other, a spring constantly opposing such rotation, a screw loosely projecting through a stationary support, a coiled spring loosely surrounding a portion of the stem of said screw and compressed between the support and a nut mounted on said screw stem, a second nut mounted on said stem beneath the support and limiting the movement of said screw through said support by said compressed spring, a third nut on said stem and projecting into the path of said lever, said lever rotating independently of said compression spring during part of its rotation by said condition responsive device, means on said lever for engaging said third nut to further compress said compression spring during a further rotation of said lever by said condition responsive device, means on said lever for operating a snap-action mechanism while it is compressing said compression spring, said means operating the snap-action mechanism in the opposite direction as said lever is rotated in the opposite direction and after it has returned said compression spring to its original position, and electric contacts operated by said snap-action mechanism.

3. In a device of the class described comprising a lever pivoted for rotation between fixed stops; a condition responsive device for rotating said lever from one fixed stop to the other, a spring constantly opp'osirg such rotation, means for adjusting the tension of said spring, a screw loosely projecting through a stationary support, a coiled spring loosely surrounding a portion of the stem of said screw and compressed between the support and a nut mounted on said screw stem, means on said nut preventing it from rotating, means for rotating said screw to adjust said nut and spring along the stem of said screw, a second nut mounted on said stem beneath the support and limiting the movement )f said screw through said support by said compi assed spring, a third nut on said stem and projecting into the path of said lever, said lever rotating independently of said compression spring during part of its rotation by said condition responsive device, means on said lever for engaging said third nut to further compress said compression spring during a further rotation of said lever by said condition responsive device, means on said lever for operating a snap-action mechanism while it is compressing said compression spring, said means operating the snap-action mechanism in the opposite direction as said lever is rotated in the opposite direction and after it has returned said compression spring to its original position, and electric contacts operated by said snap-action mechanism.

4. In a mechanism of the class described. a

lever operated from one fixed stop to the other against the action of a biasing means, a spring one end of which is attached to said lever for oscillation thereby, a U-shaped bail the bend of which is connected to the other end of the spring, a pivoted switch contact carrying lever, means on said lever for seating the legs of said bail, the arrangement being such that movement of said rst lever will cause the spring to pass over center with respect to the bail which will cause it to snap, which action in turn will align the force exerted by the bail on the switch contact carrying lever on the other side of its pivot causing it to snap, a stop, said stop comprising a leaf spring, an arm on said switch contact carrier, said leaf spring normally projecting into the path of movement of said arm, said arm camming said leaf spring out of the way on movement in one direction and engaging the edge of said leaf spring to prevent movement in the opposite direction, and means for removing said stop to permit actuation of said arm by the snapaction mechanism.

5. In a mechanism of the class described, a snap-action mechanism, a condition responsive device for actuating said mechanism, a control device, a member operated by said snap-action mechanism for operating said control device, means for adjusting the differential of said snapaction mechanism, a resilient stop comprising a normally bowed leaf spring anchored at one end and free to ex at the other, said spring normally projecting into the path of said member to oiier endwise resistance to said member and prevent its operation by said snap-action mechanism in one direction, manual means for ilexing said spring out of the way to permit such operation, and means on said member for ilexing said spring out of the way as said member is operated in the opposite direction by said snap-action mechanism, the result being that the manual means is incapable of causing operation of said control device until the di'erential of the device has been taken up and the snap-action mechanism has snapped.

CARL G. KRONMILLER. 

